1. Field of the Invention
Hemorrhagic enteritis (HE) is an economically important disease of turkeys characterized by hemorrhaging in the gut, enlargement of the spleen, depression, and often sudden death. It accounts for annual losses in the turkey industry amounting to millions of dollars. The disease is caused by a type II avian adenovirus, hemorrhagic enteritis virus (HEV), which also causes a syndrome in chickens and pheasants known as marble spleen disease. HEV is serologically distinct from all other known avian adenoviruses, and is unique among adenoviruses in its inability to grow in ordinary cell cultures. Accordingly, bird inoculation has been the only available assay for its detection and no in vitro method for vaccine production has previously existed.
This inventon relates to a successful procedure for the in vitro propagation of HEV and to the application of this procedure to the production of an HE vaccine and as a bioassay technique for determining the vaccine potency.
2. Description of the Prior Art
As reported by Domermuth et al. [Hemorrhagic enteritis. In: Diseases of Poultry, 7th ed. (M. S. Hofstad, B. W. Calnek, C. F. Helmbolt, W. M. Reid, and H. W. Yoder, eds.) pages 590-595. Iowa State University Press, Ames, Iowa (1978)], previous attempts to propagate HEV strains in conventional embryo and fibroblast cell cultures have been unsuccessful. Facina et al. [Avian Disease 26: 150-157 (1982) ] demonstrated the possible infection of chicken, turkey, and pheasant spleen cells with HEV, but all attempts to passage the virus in these cultures failed. Absent a method for the continued in vitro propagation of the vaccine virus, spleen homogenates from infected birds have been the only agents available for inducing immunity. The inherent impurity of cell-associated viruses has precluded the Federal licensing of such homogenates for commercial use as vaccines. Moreover, they do not lend themselves to lyophilization, and therefore require special facilities for storage. As an alternative to vaccinal inoculation, Domermuth et al., supra, also teaches that poults can be passively immunized by direct injection of convalescent antiserum from recovered flocks. Of course, widespread application of such an approach would be precluded by the unfeasibility of collecting ample antiserum coupled with uncertainty as to its nonpathogenicity.